My first trip to Europe was alone, and for 5 1/2 weeks.
It was an extremely great experience learning to rely on myself for everything for that long amount of time. I have since been back to Europe (with three friends) and I can say for a fact that none of the three friends I was with would have been as confident going it alone as I had been, so I think it can really depend on the person. They were really shy about asking for help and trying to interact with people, which I think really hurts the experience.
However, traveling alone (and for more than a month) really did have its down points. I found that there were many times that I wished there was someone there to share the time with me. I would meet and make friends with many people at hostels, but it just isn't the same as being with someone that you know well and who knows you. After about 4 weeks, I was simply exhausted, and got sick for a couple days, that was a really bummer to be throwing up in the middle or Romania alone.
So, I thought that going with friends was the answer, not so fast! It was also nice to have people along to share the experiences with, but after a few days, I became irritated with the people I was traveling with. I think, honestly, the worst part was compromising on restaurants to eat at, so trivial!
As has been previously mentioned, the first day in Europe can be really rough. When I was alone, I remember standing in line for the Eiffel Tower around 4 pm trying to keep my eyes open - not fun! The second trip (with friends) was much easier - we all kept prodding each other to stay up, and there was a sort of collective excitement between the four of us.
I have come to decide that the best way to see Europe would be with a significant other, but I guess I'll have to wait to find one first, huh?
Geoff